Dowel pin for concrete construction



'Oct. 5, 1937.

H. A. sHAw DOWEL PIN FOR CONCRETE CONSTRUCTION Fiq. 1

Filed Dec. 16, 1935 5 Sheets-Sheet l H ar 1 A Shaw Oct. 5, 1937. SHAW2,094,853

DOWEL PIN FOR CONCRETE CONSTRUCTION Filed Dec. 16, 1955. k I ssheets-sheet z Many. A- Shaw chm 4 Oct. 5, 1937. 4 H. A. SHAW DOWEL PINFOR CONCRETE CONSTRUCTION Filed Dec. 16, 1955 :s Sheets-Sheet -sPatented Oct. 5, 1937 DOWEL PIN FOR CONCRETE CONSTRUC- TION Harry A.Shaw, Seattle, Wash.

Application December 16, 1935, Serial No. 54,530

I 10 Claims.

My invention relates specifically to paving, and more particularly tomeans for transmission of loads from one slab of concrete paving acrossa joint such as an expansion joint, to the adjoining slab. Suchstress-transmitting means are commonly termed dowel pins, hence mypresent invention is in the nature of a dowel pin for joining andtransmitting stresses between two adjoining concrete slabs or sections,.actually or potentially separate. When I speak of slabs, however, I donot intend to exclude wall sections and the like, as my invention willbe found valuable wherever dowel pins are or should be employed, and indeed my element may be used whether there is an actual joint, a dummyjoint or line of weakening for the purpose of directing and controllingfracture, or indeed in any place where a potential or an actual joint islocated or may occur. Furthermore, while my invention will find itsgreatest field of usefulness in concrete paving, the principles thereofare valuable and applicable in other paving, as with aggregates coatedand bonded with bituminous coatings. More broadly speaking, then, myinvention relates to the reinforcement of paving or the like in suchmanner as to transmit stresses between two adjoining slabs, as broadlydefined above, whether those parts be actually or only potentiallyseparate.

My invention will be described in conjunction with paving slabs, sinceit is in this field that it will probably find its greatest use, withthe reservations indicated above, namely, that the invention may beapplied in various types of concrete. construction and in variouslocations in any such construction.

It is customary in such paving construction to employ in the so-calledexpansion joint between slabs a filler strip which hasa number of holesthrough it, in which holes are received steel dowel pins, so that whenthe concrete is poured on either side of the expansion strip, the endsof the steel dowel pins become embedded in the adjoining edges of twodifferent slabs. To provide lengthwise slippage, one end of the dowelpin is greased and painted, so that as the concrete expands or contractsat a rate different from the rate for the pins, slippage will occur atthis treated end because the painting and greasing breaks the bondbetween the pin, and the concrete. Theoretically, then, these dowel pinswill transmit stresses between the two slabs, so that they mutuallysupport each the other. In practice, however, it has been found thattheir action is considerably more complicated than this. Due to climaticor atmospheric changes, the concrete tends to contract and expand, or tocurl, and thus the rigid steel dowel pin, which expands .and contractsat a diiierent rate, and which cannot curl, acts as a rout or drill togrind away the concrete immediately surrounding it, and thus to enlargeits hole, and this action is progressive as time passes. Moreover, thehole being enlarged, room is permitted for play, so that as the concreteslab is flexed slightly by the passage of traffic, it begins to poundupon the steel dowel pin, which acts as an anvil, and this again breaksdown the concrete immediately surrounding the pin and progressivelyenlarges the hole and weakens the slab. When any enlargement of thehole, surrounding the dowel pin, occurs there is a reduced area ofbearing of the concrete on the round dowel pin. This concentrates loadson the concrete along a small area, resulting in a more rapid crushingaction, later in bending of the dowel pin, and progressive deteriorationof the concrete. 7

While these difficulties have been recognized, .and efforts have. beenmade to avoid them, as mentioned above, by coating one end of the dowelpin with bitumen or by encasing it within a cap, so that play ispermitted lengthwise of the dowel pin, as the concrete expands andcontracts, this has been found not altogether satisfactory, particularlyso as the dowel pin must be precisely parallel to the direction ofexpansion and contraction, or otherwise a bending moment is setup in thedowel pin, further tending to grind away and break down the. concrete,and from the manner of embedding these dowel pins in the slabs, theybeing held merely by their projection through the rather flimsyexpansion strip material, it is, practically speaking, impossible tohave all such dowel pins, or any considerabl'e number thereof, preciselyin line with the direction of contraction and expansion. Moreover, asthe rate of contraction and expansion varies in different slabs, owingto their being exposed differently to shade and sun, they will notalways expand and contract along longitudinal lines; hence even thoughthe dowel pins may be set precisely longitudinally, they may still tendto be bent under some circumstances.

Furthermore, if these steel dowel pins are once bent beyond theirelastic limit, they tend always a accelerate such cracking.

Steel dowel pins being, of necessity, rigid, but

the two slabs joined thereby being repeatedly flexed by traffic, or byatmospheric conditions,

these dowels may, of themselves, constitute a potentially destructiveforce, in that they may hold the edges so rigidly in alignment thattheir elastic limit is exceeded, and they crack around that is, outsideof-the dowels.

So many difficulties have arisen from the employment of such dowel pinsthat their use is being discontinued in some new constructions, it

being felt that the disadvantages (including cost) rather outweighed theadvantages of using them. There are, however, certain advantages,theoretically at least, in that each slab. will cooperate with adjoiningslabs 'to mutually support the traffic loads as they pass from the edgeof one slab onto the edge of the other, and these are particularly theweak points of such paving slabs, owing to the fact that the concrete,being exposed to sun, snow, and other extremes of weather, will curlaway from the subgrade, or the latter from repeated pounding will bepermanently compressed, orwill settle, so that the slab will at timeshave its edge unsupported by the subgrade, the latter being affectedmore slowly and to a lesser extent by weather and climatic changes thanthe slabs. Therefore, to retain the advantages of dowel pins, yet'toeliminate their disadvantages, is the general aim of the.

present invention.

A still further object of the invention is to utilize a material whichis a waste material, and therefore cheap, a material which is eminently7 suited to the purpose, and of which there are large quantitiesavailable in all parts of the country (and will be, so long as there areroads), namely, tire bead material.

The casings of tires, less the beads, may be used for a variety ofpurposes. They may be stamped into various shapes, and thus used, as'

for example, in the making of mattings or marine fenders. They may beground up and the rubber reclaimed or reused. In" manufacture'of thetire bead the material is subjected to tre-' mendous pressure, greaterthan any other part of the casing, is of the purest rubber compound ofany in the tire casing, and incorporates many plies of the finest cottonfiber manufactured into cord or fabric strips. Moreover, it incorporatesgroups of steel wires of high flexibility and strength, and this is inall cases surrounded by a matrix of rubber, usually a high grade rubbercompound which impregnates the group of wires and all the plies of thefabric. Such tire bead material, then, incorporates the finestmaterials, but it has never heretofore found any practical use on a'large scale, and is so constructed that it is difiicult or.uneconomical'to reclaim the rub- My invention is illustrated in theaccompanying drawings, in various forms, and illustrating Various waysof employing the invention.

Figure 1 is a plan view of half of a typical road, illustrating a simplemanner of using my invention.

stances steel dowel pins may act to cause and Figures 2, 3, and 4 aresimilar plan views, each showing a modified way of using the invention.

Figure 5 is a plan view, on a somewhat enlarged scale, of part of anexpansion joint and the two adjoining slabs, illustrating a furthermodification.

In all the above views parts of each slab are broken away and shown insection. v

Figurefi is a vertical section through two adjoining slabs at theexpansion joint, illustrating the dowel pin in place, parts being brokenback and shown in section.

Figure '7 is a view similar to Figure 6, showing my dowel pin employedin a dummy joint.

Figure 8 is a sectional View on a generally horizontal plane, throughsuch a dowelpin and the two adjoining slabs.

Figure 9 is a transverse section through a typical tire bead.

Figure 10 is an elevation and part section of such a dowel pin in place,showing an anchoring means Whichmay be employed in connection therewith,and Figure 11 is a similar View showing a modified disposition of theanchoring means.

' Figure 12 is a view similar to Figures 10 and 11, showing a stillfurther modification of the anchoring device.

When I refer to tire bead material I refer to material whichincorporates at least that part of the tire casing usually termed thebead, and

' which, as shown in Figure 9, usually consists of a bundle of wires Hembedded within and impregnated by a matrix of rubber compound, asindicated at i2, this in turn surrounded by several plies of fabric atl3, sometimes incorporating a mass of rubber compound at I4 to shape thebead, outer plies l 5, and sometimes an outer layer of rubber compoundat IS. The group of wires at H may be merely a single wire or rod, wireslaid side by side, or a plurality of twisted wires, or they may bebraided into a stranded cable. Furthermore, when I refer to tire beadmaterial it is not essential that allthe elements named remain in thematerial as used, for it is possible to withdraw the wires II, forexample, and while they are valuable in reinforcing and stiffening thematerial, the fabric plies nevertheless give it, great stiffnessand'strength, and it will still be valuable without the wires.Furthermore, there may be more or less of the side wall material left inplace upon the bead. As a minimum requirement, the term tire beadmaterial as used in this specification must incorporate a strong core ofstress-transmitting material, such as wires or fabric plies, embedded ina resilient shroud, such as rubber, and which therefore can not easilybe permanently deformed by sub-v jection to repeated and materialstrains.

The bead material would ordinarily be cut into lengths suitable for thepurpose intended, but as will appear in Figure 4, I may at times employthe complete circular tire bead as a reinforcement,

or as a dowel across joints.

In Figure 1 the slabs, designated 2, 3 and 4 to distinguish them, arepoured in place on the subgrade, with expansion joints between them atintervals, at 23, and 34, respectively, and there may also be dummyjoints 3| and 32 formed in the slabs to provide weakened lines so that,if the slabs crack, the cracking will occur here and will be localized.My dowels may be placed across the dummy joints as well as across theexpansion joints. They may also be used along the longi- These expansionjoints are indicated tudinal joints, and in general in any place, wherethere is or later may be two separate pieces.-

As is seen in Figure 1, the dowel pins l, formed of tire bead material,may be put-in place by embedding them within the expansion stripe atintervals, or otherwise sup-porting them in the forms,.so thattheyproject into each slab 2 and 3. Owing to their cheapness, as manymay be used as desired. It is not so necessary that they be asaccurately placed as steel dowel pins, as they are inherently yieldableand elastic, nor is it necessary to provide an expansion spacelengthwise of these pins, as they are compressible longitudinally. Asthe slabs are poured, with the expansion strip 5 in place, thedowel-pins I will become embedded in each adjoining panel or slab.Preferably they extend lengthwise of the paving, in. expansion,construction, or dummy joints, and transverselyin longitudinal joints.As shown in Figure 1,..they are all of the same strength. and equallyspaced. Angularly spaced dowel pinslic are shown at the corners ofpanels, for the purpose of reinforcing the corners which are weak spots,and to hold parts together should breakage occur. However, it may bedesirable to particularly strengthen certain parts of the joint, and inFigure 2 the dowel pins of the transverse joints are shown as all of thesame strength and size, but more closely spaced at' 'certain parts ofthe joint than at others. In Figure 3 there are shown equally spaceddowel pins, but the pins la are stronger and heavier than other pins lb.In Figure 4 is illustrated the use of complete tire beads, uncut exceptas they are cut away from the tire casing. Thus at ii! are showncomplete tire beads embedded in the concrete, either across the falsejoint 32 or in the corners of the slab. Dowels I may be employed in thesame manner as before, or the circular beads It} may be extended acrossthe expansion joint, if desired. Since concrete paving slabs frequentlytend to break off across the corners it will be desirable to insert tirebead rings ll] in the corners of the slabs, to reinforce these cornersand to serve as dowel pins should breakage occur.

These beads, made from heavy tires, are of considerable thickness, andsince the expansion joint is ordinarily from one-half to three-quartersof an inch in width, the dowel pins in transverse joints may be placedtransversely of the slabs, that is, lengthwise of the joint, as shown inFigure 5, instead of transversely of the joint. Such an arrangement isillustrated, the several connectors I! being placed in the joint betweenthe slabs 2 and 3, embedded partly in each slab.

While the precise manner of locating the dowel pins of tire beadmaterial is immaterial, and it is immaterial whether they be preciselylengthwise of the direction of expansion and contraction, yetpreferably, to take advantage of their curved form, they are placed insuch a manner that the plane of their curvature is vertical, that is,their concave side is down, as seen in Figures 6 and 7. In Figure 6 sucha dowel pin l of tire bead material is shown located between two slabs Zand 3, with expansion strip material 5 between them. The slabs areassumed to have expanded. They tend thus to compress between them theentire length of the dowel pin, the surfaces of which slip with relationto the concrete in contact therewith, and this material, being of rubbercompound, is elastically yieldable. It compresses more or less uniformlythroughout, but upon contraction of the slabs 2 and 3 it will againresume its normal position. Because of the elasticity of the materialwhich comprises the tire bead dowel pin, it may yield in all directionswithout being permanently deformed. If the slabs 2 and 3 contract, toseparate more than they were when poured, each dowel pin slips in itshole, later resuming its normal or initial position, all withoutabrasion or wearing away of the concrete. The factors of expansion orcontraction of such dowel pins-need never be taken into consideration,as their compressibility and elasticity will take care of such factors.

Such dowel pins being non-rigid, as pounding stresses are communicatedtoit by the passage of traflic'from one slab to the other, it will notform an unyielding anvil, but rather will yield slightly, though stillaffording adequate mutual support between the two slabs. Since it doesnot wear or grind away the concrete surrounding it, the area of supportis never lessened. If it is not put in place perfectly parallel to thedirection of contraction and expansion, as shown in Figure 8, it willnevertheless yield, due to its inherent elasticity and flexibility,without grinding'on the walls of its socket or the edges of the slab,

and will always tend to return to its normal position. Thus at A and Athe material is shown as pressed inwardly, contracted, due to a forcetending to separate the two slabs 2 and 3, and at B and B it is shown asexpanded somewhat, but because there is no hard material in contact withthe concrete at these points, there is no wearing away of the concrete.Nor can there be any permanent bending of the wire I l, which acts as abeam, as this is embedded in rubber and rubberimpregnated fabric.

It may be desirable in some instances to lock the dowel pins in theslabs, and in this way to somewhat limit their extension or contraction.To this end, as shown in Figure 10, I may employ pins, preferably ofsteel or like metal, as shown at 6, passed transversely through the endsof the dowel pins l prior to their embedment, so that the cross pins 6will be embedded in. the concrete. By placing these cross pins 6 nearthe ends of the dowel pins l, the latter are permitted the maximum ofexpansion and contraction. By placing the cross pins 60 in Figure 11closer together the expansion and contraction of the tire bead dowelpins is lessened.

The tire bead material might be made use of as an anchor, as is shown inFig. 12. Here a length iii of tire bead material is used as a cross pinpassed through the eye 62 of a steel dowel pin 63. This still takesadvantage of the contractability and yieldability of the tire beadmaterial at 6! while yet providing a steel dowel pin across the jointbetween the two slabs 2 and 3.

It is illogical to provide a dummy joint, where fracture is to occur iffracture is unavoidable (usually by fatigue resulting from repeatedflexure) yet to provide a rigid steel dowel pin across the'dummy joint,so rigid that it tends to prevent fracture in the joint. This sometimesresults in the fracture extending, uncontrolledly, around the ends ofsuch dowels. Moreover, after fracture has occurred, such steel dowelpins aggravate conditions and tend to increase material will conservethe material, transmitting stresses from slab 3 to fractured piece 30without breaking down either.

What I claim'as my invention is:

1. Means for transmission of stresses between two adjoining concreteslabs, comprising a piece of tire bead material, partly embedded in eachslab.

2. Means for transmission of stresses between two adjoining concreteslabs, comprising a length of tire bead material, one end of which isembedded in one slab, and the other end of which is embedded in theother slab.

3. Means for transmission of stresses between two adjoining concreteslabs, comprising a group of'wires embedded in rubber compound andconstituting a dowel pin, whereof one end is embedded in one slab andthe other end in the other slab.-

4. Means for transmission of stresses between two adjoining concretepaving slabs, comprising a length of tire bead material, disposed acrossthe joint between slabs with its concave side down, one end of suchlength being embedded in one slab, and the other end being embedded inthe other slab,

5. Means for transmission of stresses between two adjoining concreteslabs, comprising a length of tire bead material, opposite ends of whichare embedded in the respective slabs, and cross pins secured to each endof the tire bead length, and embedded in the respective slabs.

6. Adowel pin for use in paving or like concrete construction,comprising a length of tire bead material.

'7. A dowel pin for use in paving or like concrete construction,comprising an integrate stress-transmitting. core incorporating overlaidfabric plies, which core is impregnated with rubber and vulcanized intoa stiff, yet elastically yieldable bar.

8. In combination, two adjoining concrete paving slabs having anexpansion joint therebetween, and a plurality of dowel pins extendingacross said joint at intervals, formed of lengths of tire bead material.7

,9. Means for transmission of stresses between two adjoining concreteslabs, comprising a composite member uniform throughout its length,including a stiff beam embedded in and integral with a cushioning shroudof resilient material, one end of said member being embedded in oneslab, and the other end thereof being embedded in the other slab.

10. Means for transmission of stresses between two coplanar adjoiningconcrete slabs, comprising a stiff beam, having bonded thereto an outercushioning surface of rubber compound elastically yieldable understresses transverseto the beam.

' HARRY A. SHAW.

